Production of artificial bristles



2 Sheets-Sheet 1 Filed June 15, 1945 &

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INVENTORS larwy l1. Neville BY 7710/1145 6. Harris IITTO/IWEY (H. A.NEVILLE ETAL Y 2,426,896 PRODUCTION OF ARTIFICIAL BRISTLES Sept.2,-1947.

' 2 Sheets-Sheet 2 Filed June 15, 1943 H i L w i! .L i E T. m a

. v a mu mlw INVENTORS flan/(q Mm!!! y Thu/n4: 6. Harris Patented Sept.2, 1947 PRODUCTION OF ARTIFICIAL BKISTLES Harvey A. Neville and ThomasG. Harris, Bethlehem, 2a., asslgnors to Devoe & Baynolds Company, Inc.,a corporation of New York Application June 15, 1943, Serial No. 490,928

9 claims. (01. 111-1) In United States Patent No. 2,267,597 a process isdescribed for making artificial bristles by a batch process. A method isalso illustrated schematically for making these bristles continuously.The apparatus and methods there indicated are capable of producingbristles ona limited basis, but we have found that substantialimprovement over and above the processes therein set forth are necessaryor valuable in order to produce, bristles on a volume production basis.This application is a continuation in part of our earlier applicationSerial No. 432,-.

594, filed February 27, 1942.

In the continuous commercial production by our process of syntheticbristles for paint brushes having tapers to correspond with naturalbristles, a plurality of filaments are passed through an appropriatecoatingbath'in such a way that the speed of movement of the filaments isvaried as they emerge from the bath so that the coating will form zonesof varying thickness on the filament cores. Subsequently the coatingsare dried and hardened.

In this application, the term filament is used todesignate the core onwhich the coating is built up.- Such a filament may be a single integralstrand, but ordinarily it will be built up of a large number of strandsof fibrous material twisted together to form a thread. For example, wehave obtained excellent results using a 150 denier yarn made up of 40-separate rayon strands. termed a 150 denier, 40 filament yarn, we usethe term filament as applying to such an entire yarn or to other typesof core material that may be used as referred to in the earlier patentspecified.

In order to produce the bristles on an economical basis it is essentialthat a very large number of filaments be operated continuously through acommon device. For example it has been found eflicient to operate asmany as 800 filaments simultaneously through a single apparatus. Inorder that these can eventually be cut up into the appropriate bristlelengths at the right points, they should be kept accurately in registerand each strand of bristles should be substantially similar to theadjacent ones. The present invention relates to methods whereby this isaccomplished.

In carrying out this operation, we have found that a, number of featuresare important:

(1) A large number of core filaments are simultaneously passed in andout of a coating bath containing some appropriate plastic which willWhile such a thread is sometimes cling to the surface,

and as these filaments emerge from the bath their speed of movement isconstantly changing from a slow movement to a more rapid one and thenback to the slow movement again. When the filaments are moving rapidly,they carry with them a relatively heavy coating of material and thefinal bristle is relatively thick at the point which emerges from thebath at the higher rate of speed. As

1 the speed of the filaments slows down, the coating gradually decreasesin thickness until a minimum thickness of coating is-obtained at thepoint of minimum speed. The speed then accelerates and the coating againbecomes heavier.

As the coated filaments leave the coating bath, they are given apreliminary drying and subsequently are passed through a final baking orhardening oven. We find that it is quite important that during thisfinal hardening step the coated filaments be kept under substantial andpractically constant tension, and as a practical matter we have found itefficient that they should be drawn through the baking oven atsubstantially uniform speed. In order to permit of 5 this we find thatit is advisable to use an apparatus which gives to the coated filamentsa basic speed rate and then interposes in the movement of suchfilaments, at a point somewhere between the coating bath and thehardening oven, a device which alternately accelerates and slows downthe speed of the movement of the filaments through the coating bath andyet feeds them at the basic speed rate to the drying oven where they arehardened under tension. In

order that the coated filaments may not be distorted, it is desirablethat they be given a preliminary drying at the variable speed rate sothat the coating is sufiiciently hard to permit it to be gripped at theuniform speed rate to maintain the proper tension in the baking oven.After the coated filaments have been dried and hardened under tension,they are cut into bristle lengths at approximately the points of maximumand diameter.

Generally speaking, we accomplish our control of speed by having thefilaments run upwardly out of the coating bath through a preliminarydrying zone and over a speed-control roller. From the speed-controlroller the coated fila- 5o ments run at a substantial angle (preferablyapproximating a right angle) ofi to the side where they are grippedbetween driven rolls operating at a constant speed. The speed-controlroller is an idler roll, but mechanism is provided so that thls roll canbe reciprocated up and down in 3 order that it may periodically approachand then move away from the coating bath. As it approaches the coatingbath the speed of movement of the filaments through the coating bath isreduced and as it moves away from the coating bath, this speed isaccelerated. Obviously,

the speed of movement of this control roll should which the coatedfilaments next pass. This distance can be maintained actually constantby mounting the speed control roll on arms pivoting about a pointconcentric with such an adjacent roll, but the distance will ordinarilybe sufficiently uniform if the speed-control roll reciprocates in astraight line back and forth toward the coating bath and the filamentsrun from the speed control roll in a direction which is approximately atright angles to the line of movementof the speed control roll.

The length of the finished bristles can be varied by changing the timeor period of movement of the speed-control roller relative to the basicspeed of the filaments, and then varying the cutting mechanismaccordingly.

This mechanism is one which we have found efiicient for passingthefilaments at variable speeds through the coating bath and then con--tinuously and without interruption feeding them through a set of rollswhich operate at constant speeds. We do not intend to suggest that thisis the only form of mechanism that may be employed for this-purpose, forobviously there are mechanical equivalents of the system suggested. Forexample, the filaments could pass in a straight line from an idler rollto a pair of rolls driven at constant speed and an additional idler rollcould be supplied which would periodically press against the coatedfilaments between these rolls to force them out of their straight linemovement and, then permit them to return.

In any event, the-important feature is that means be supplied fordrawing the filaments through and from the coating bath at speedsvarying at predetermined rates from a minimum to a maximum and then fromsuch maximum back to the minimum in a substantially .uniform cycle toform coatings comprising a series of tapers, with an opportunity beingprovided to permit such coating to gel, and that-means be then suppliedso that the coated filaments can pass progressively through a hardeningoven while held under substantial tension. Further, we have found thatthe tension during final hardening should be exerted on the filamentswhen they emerge from the bath at their slower speed.

The initial gelation of the. coating is the result of a relativelyslight evaporation of solvent accompanied by a drop in temperature andtakes greater than the tension place very rapidly with no greatshrinkage in a volume. As a result, no great amount of tension isnecessary to hold the filament straight at this time. Since unnecessarytension at this point increases the mechanical difiicultieathe tensionthrough the first gelation stage should be only such as is necessary tocause the fila- 'ments. It must be borne in mind not.

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curl, and this is particularly noticeable if the humidity is high. Inthe final hardening operation, a relatively large amount of solvent mustbe driven out of the coating which causes it to shrink. During thisstage of the process, a dlfierent and substantially increased tensionmust be provided. This means that two sets of tensioning apparatus haveto be employed, and we have found it advantageous to associate thevariable speed mechanism with the first set so that when the filamentsare passing through the hardening oven they move at a substantiallyconstant speed.

' (2) With the work which we have done to date, using a coating bath inthe form of a solution, we have found that if the coating is to becapable of being applied with variable thicknesses according to aconstant cycle, the bath should preferably be very close to the gelationpoint so that the coating material gels almost immediately upon thewithdrawal of the filathat this operation involves substantially morethan the formation of a thin surface film, for at the thickest pointsthe finished coated product has a diameter several times thicker thanthe diameter of the core filament.

Certainly the bath should be sufiiciently viscous to permit theformation of a coating averaging at least as thick as the diameter ofthe uncoated filaments. Using a coating bath in the form of a solution,this is best accomplished by having the concentration of solids kept ashigh as possible and by operating at a slightly elevated temperature. Bymaintaining these conditions a coating of'desired thickness can beformed. Also by maintaining the maximum permissible concentration ofsolids, less distortion of the bristles (particularly in their thickerportions) takes place on drying. While the bristles made by this processhave the general shape and conformation of natural bristles, a magnifiedexamination will show that the shrinkage due to the evaporation ofsolvent causes some distortion in the cross-sectional shape. It isadvantageous to keep this distortion reduced to a minimum and this canbest be accomplished by maintaining the concentration of solids veryhigh relative to the amount of solvent employed.

\to the gelation point, the surface may gel suificiently to form skinsor films. These may extend between the emerging filaments so that massesof the surface are picked up and spoil the prod- In the former patent itwas stated that the container for the coating bath must be filled asnear the top as possible to eliminate a. surface layer of vapor. We havefound that with continuous production using a large number of filaments,the

direct opposite is true, and the bath can be mainrtained sufficientlyconcentrated and sufiiciently close to the gelation point and yet notform surface skins, only if a vapor layer or blanket of appreciablethickness is maintained over the surface of the bath and if the bath ismaintained at the desired temperature close to the surface where thefilaments emerge. These results are best obtained by the use of acontrolled atmosphere over the bath, preferably assisted by the use ofheating coils in the bath.

We have found that the vapor layer (due to the fact that it is heavierthan air) can be adjusted and maintained by supplying a wall or damaround that portion of the surface of the liquid from which thefilaments emerge, and by adjusting the height of this dam above theliquid surface. This can be done either by maintaining a constant, levelin the coating .bath or by floating the dam in the coating solution.Ordinarily this dam will run around the whole group of emergingfilaments, but if desired separate'dams may be employed for groups offilaments or for individual filaments. In such case, the dams do notneed to be as high as we otherwise specify herein, as the vapor layer ismore localized. The use of these smaller dams adds somewhat to thecomplexity of threading upthe machine. In an" event, the dam must beclosely adjacent to the outer linesof the points of emergence of thefilaments and the surface of the coating fluid should she kept free fromdrafts. When working on a large number of filaments, if one attempts toblow air through them as they emerge from the coating bath, we havefound that it is extremel difficult to prevent the formation of skins orfilms over the surface of the coating bath.

The critical point of the whole operation is here at the surface of thecoating bath, and many variables must be properly interrelated to carryout the operations successfully. If the bath is not sufiiciently closeto the gelation point, the coating material will fiow on the surface ofthe filaments and form beads or droplets. If the filaments are too closetogether or move at too high a rate of speed, they will tend to lift thesurface of the bath which will form strings or skins running from onefilament to another. This danger is exaggerated if the rate ofevaporation is increased on the surface of the bath, or if it ischilled.

It is only by the use of the protecting vapor layer and careful controlof temperatures that we have been able to coordinate these factors togive satisfactory commercial results, for the bath which we prefer touse is one so saturated that it would immediately form a surface skin ifcooled to room temperature and exposed directly to the air. Thusemploying a bath of cellulose acetate dissolved in acetone andmaintained close to its gelation point, at a temperature of about 50 C.,

and employing a vapor layer of substantial thickness, we are able tomove the filaments through the bath at an average speed of as much as3.5 feet per minute and to have these' filaments as close together as ofan inch apart in rows, with the rows spaced about of an inch apartwithout forming skins and without the coating liquid flowing to formbeads.

Ordinarily the limits of the rate of speed of movement through thecoating bath will be between a minimum rate not below a value over zeroand a maximum not greatly exceeding 10 feet per minute, that is, theaverage speed will be not more than about 5 feet per minute.

The thickness of this vapor layer may be considered to be approximatelyequal to the height of the dam or rim around the bath above the sur-"face of the bath, and we have found that to get commercial productionthis should be at least /2 of an inch and preferably between of an inchaeaasoe 6 and 1 inch in height' In operation, the aim should be tomaintain the vapor layer just as thick as possible without causing thecoating to move on' the filaments to form beads or droplets.

In some cases when a bath has been running with entire satisfaction, itmay suddenly indicate a tendency to form skins on the surface. Thisprobably is due to a change in the vapor layer such as may be caused bysome sli ht draft or by a change in the relative humidity or by someother factor affecting the rate of evaporation of solvent. If such askin formation is -indicated, the operator may have additional solventavailable which can be sprayed over the surface of the bath to increasethe concentration of the solvent vapors over the bath surface and alsoto lower its viscosity.

(3) If the coating is applied to the filaments from a bath where thecoating material is in solution and very close to the gelation point, itwill mean thatthe bath is sumciently viscous so that ordinarily therewill not be sufilcient opportunity for the coating material in the bathto work its way through between the various fibers or strands that go tomake up the basic core filament.

In the issued patent already referred to, it was suggested that thesecore filaments might be impregnated with thermo-setting resin whichshould be hardened before the coating is applied. We have found that itis much better to subject the filaments to a preliminary impregnation ofplastic material which is not set-up before it reaches the coating bath.This may be a thermo-plastic material or a thermo-setting material or amixture of the two, but if a thermo-setting material is employed for thepreliminary impregnation, we have found that it should be kept in its Bstage so that it is capable of being softened in the coating bath. Alsothe material used for impregnating should be compatible with r thematerial used for coating so that a firm bond or coalescence will be hadbetween the two. Actually, we have obtained the best resultswhen theimpregnating bath is made up at least in part from the same plasticmaterial as is employed in the coating bath.

While'we refer to the filament as being impregnated in this first bath,we do not mean that this treatment must actually penetrate into theseparate strands. It is rather a case of having the impregnating bathenter the filaments between the various strands so that these arecemerited together to form a unified filament to which the coating canreadily adhere. By controlling the degree of this impregnation, bristlescan be made which in use will fray out slightly or flag at their tips.This is highly important, for a proper flag on the bristles greatlyimproves the evenness with which paint will flow from the finishedbrush. The amount of impregnation should be suificient to bond togetherthe separate strands and serve as a base for the finishing coat, but nottoo much to prevent such fiagging. The ability of the bristle to "fiagproperly is also assisted by having the outer coating quite thin at thetip end. The desired result can be assisted by varying the concentrationof solids in the impregnating bath.

After the filaments leave the impregnating bath they should be permittedto dry sufiiciently so that the impregnating material will gel, but if athermo-setting material has been used for the impregnation, it ispreferable that it should not be hardened to the point where it willset-up which we have found on the Gardner-Holdt scale (at 25 0.).

and thus not soften to serve as a base for the coating material.

- By giving the filaments this preliminary 1m pregnation with plastic:material that is compatible with the coating material and whichpreferably is soluble in the solvent of the coating bath, we have foundthat the filaments need to stay in the coating bath only for a briefinterval of time and that there appears to be very little difference inresult if some of the filaments remain in the coating hath through alonger path of movement than others because a good bond for the coatingis had almost immediately. This simplifies the mechanical arrangementsof the process.

Our tests have indicated that where we employ a preliminary impregnatingbath which is compatible with the coating material, the bristles willhave a relatively long life and withstand substantial flexing. On theother hand, where the coating is not bound to the filaments through themedium of the impregnating material, there may in some cases be atendency for the coating to split and crack oil from the filamentsinuse.

The coating bath employed is a solution of a resinous film-formingmaterial so constituted that as the filaments emerge from the bath, thecoating will gel quite rapidly. As previously stated, this ordinarilydemands the use of a volatile solvent, and the maintenance of thesolution just short of the gelation point. However, the factorsaifecting gelation vary with difierent types of resin.

In United States Patent No. 2,267,597 already' referred to, a number oftypes of coating compounds are suggested, and various other resinousbodies may be employed provided they have the proper characteristics tomeet the particular service demanded. Jne coating compositionexcellently adapted for use in our process consists of a mixture ofequal parts of high viscosity and low viscosity cellulose acetate and aplasticizer such as dimethyl phthalate or other similar type ofplasticizers known in the trade, in an amount equal to about 10 or 11%of the cellulose acetate. These materials are dissolved in a volatilesolvent such as acetone to give a viscosity ranging from Z1 to Z2 Ifdesired, some methyl alcohol may be used with the actual solventmaterial and the solutions otherwise modified as is known to thoseskilled in the art. A solution such as we have specified isadvantageously employed at a temperature of from about 10 C. to C. aboveroom temperature, as for example a temperature of about 50 C. In somecircumstances, we have found it desirable to incorporate athermo-setting resin with the thergno-plastic material, and for thispurpose have employed furfuryl alcohol which has been given a partialpolymerization. However, this adds somewhat to the complexity of theoperation and we have not found it essential in order to producesatisfactory bristles. In some cases we have employed such a mixture,diluted to a low viscosity, in the preliminary impregnating bath andhave used the acetate composition, without the furfuryl alcohol, in thecoating bath. This has given good results.

By-combining these various features we are able to make bristles withcommercial rapidity which are cut oif and collected insubstantialbunches so that they can readily be made up into.

paint brushes.

may be The operation of our process and the machinery which we haveemployed for carrying it out are illustrated in the accompanyingdrawings in which Fig. 1 shows a side view of the apparatus with thedrying oven illustrated in section. Fig. 2 is a perspective view ofcertain of the moving parts; Fig. 3 is a sectional view on an enlargedscale through the coating bath; Fig. 4 is a sectional view taken on line4-4 of Fig. 3; Fig. 5 is a sectional view greatly enlarged of atypicalfinished bristle after some use (with the center broken away) and Fig. 6is an end view of the bristle of Fig. 5.

The base filaments I0 are wound on a drum II, the rotation of which iscontrolled by a brake band l2 which is adjustable so that proper tensioncan be maintained on the filaments. The filaments pass over a roller M,then under a roller [6 into the preliminary impregnating bath l8. Fromthe bath l8 the filaments pass up over the roller 20 and down to thecoating bath 22.

The coating bath 22 comprises an inner vessel 24 to hold the actualcoating liquid. In this are arranged a series of bars 26 each of whichcarries a number of guides 21. The strands pass through- 4 the guides asillustrated and up out of the coating bath.

In order to maintain the liquid in the coating bath at a desiredtemperature there is an outer shell 28 serving as a jacket to receiveoil or other heating media. This oil is heated by any desired means suchas the coils 29. Additional coils 30 are preferably supplied passingthrough the actual liquid in the heating bath to carry hot oil thevessel 24 is carefully controlled and ordinarily should range at aheight of from one half inch to one inch below the top edge of thevessel 24. This serves to maintain a layer of vapor over the bath whichtends to prevent the formation of skins.

From the coating bath 22 the coated filaments pass upward to apreliminary drying oven 3| where the'filaments are dried sufiiciently sothat they can be passed over other rollers without undue distortion orsticking. This oven is heated in any desired manner to a temperature ofabout C. The coated filaments pass over a movable roll 32, which rotatesin slide blocks 34 (see Fig. 2) which reciprocate in hangers 36 (thehangers 36 are omitted from Fig. 2 for the sake of clarity). Due to thereciprocation of the roll 32 the speed of withdrawal of the filamentsfrom the coating mm 22 can be varied in a predetermined manner to formtapered'filaments.

After the coated filaments have passed over the roll 32 they go aroundroll 38 and then through between the driven rolls 40 and thence passinto the drying oven 42 where they go back and forth a number of timesso that they can be adequately hardened. The drying oven 42 ismaintained at a desired temperature (for example, about C.) by heatingmeans not shown.

When the filaments emerge from the drying oven 42 they pass over a roll44, thence around the tensioning roll 46, over the roll 48 and throughthe driven rolls 50. After coming out of the driven rolls the filamentsare cut to,length by any desired mechanism not shown.

The rolls 40 are driven from a. jack shaft 52 which in turn is driven bya motor 54 acting through gear reduction mechanism indicated at 56 and aspeed control mechanism 58.

Likewise driven from the jack shaft 52 are the crank wheels 60 to whichare attached the connecting rods 62 that control the reciprocatingmovement of the roll 32. The degree of this movement is controlled bythe degree of eccentricityof the attachment of the connecting rods 62,and this is adjusted by the screws 64. It will be noted that by turningthese screws 64 this eccentricity can be reduced to zero so that therewould be no movement of the rolls 32 in which case the filaments wouldbe withdrawn from the coating bath 22 at constant speed and thereforewould have uniform diameter.

The tension from the drum ll through to the rolls 40 will depend uponthe friction generated by the friction band l2 and in general thistension should be only enough to prevent the filaments from sagging orbecoming entangled; for example this may amount to between one halfounce and two ounces per thread. On the other hand, the tension on thecoated filaments as they pass through the hardening oven 42 will besubstantial due to the action of the tensioning rollers 46 and mayamount to about 5 ounces per thread. The rollers 50 which draw thecoated filaments through the hardening oven 42 are driven by-a motor 66operating through gear reducing mechanism 68 and a speed controlmechanism ill, The speed with which the filaments are withdrawn from thecoating bath will alter the thickness of the coating and the averagespeed can be adjusted readily through the speed control mechanism 58.Obviously, the speed with which the filaments are finally withdrawn mustbe coordinated with the average coating speed, and this is done by thespeed control mechanism 10. 1

It will be noted that while the filaments in general pass through thecoating bath at a constantly varying speed ranging between a,predetermined minimum and maximum they are brought to a substantiallyuniform speed before entering the hardening oven 42 and are then placedunder an increased tension so that they will dry and hardensubstantially straight.

The length of the final bristles will depend upon the rate ofreciprocation of the roller 32 relative to the average speed. In thdrawings no mechanism is shown for varying this relationship butobviously if bristles of a different length are to be made the variationcan be controlled by varying the size'of the pulley wheels on the jackshaft 52.

By operating as outlined above, we have found it possible to produce onan efiicient commercial basis bristles which taper so that they have anexternal shape and size that approximates that of a natural bristle.They further have the added advantage that when these bristles are usedin a paint brush, the tips fray out slightly to form a flag (somewhatlike that of natural bristles) which provides a mopping action andcauses the paint to flow on very evenly. This effect is illustrated inFigs. 5 and 6 which indicate a typical bristle greatly enlarged. InFig.5 the central part of the bristle is broken away, as a bristle ofthis diameter if shown in full proportion would be very long.

In these figures the base filament II] is indicated as made up of atwisted yarn comprising a number of strands. The impregnating resin isnot specifically indicated, but the coating resin is designated by thenumeral 12. It will be noted in Fig. 5 that this varies from a very thincoating near the tip toa coating at the butt which has an averagethickness considerably greater than the diameter of the filament Ill.Due to this taper, the bristles have the general shape and size of thenatural bristles but an enlarged view shows that they are not absolutelycircular in cross section. Particularly at the base where the coatingmaterial is thick, the evaporation of solvent and shrinkage may causesome distortion and a typical butt end section might have an appearancesuch as is indicated in Fig. 6.

When the bristle has been used for a short time, the coating near thetip breaks away and the core filament l0 frays out to form the flag 14.

These bristles have a substantial water resistance and with reasonablecare resist the" action of the solvents contained in the paint so thatthey have a good commercial life. By using the features shown in thisapplication, they can be produced at relatively low cost and they makepaint brushes which apply paint in a very efiicient manner.

It is understood that the specific details given are intended only byway of illustration and that the same may be modified in manyparticulars without departing from the spirit of our invention.

What we claim is:

1. A continuous process of making tapered bristles which comprises thesteps of passing a plurality of continuous core filaments into and outof a coating bath of plastic material which is sufiiciently viscous tocling to the filaments to form coatings of substantial thickness and notto run substantially on the filaments as they are withdrawn,intermittently varying the speed with which the filaments emerge fromsuch bath between a minimum rate of speed which involves positiveforward movement and a maximum rate of speed not in excess of ten feetper minute, followed by a variation from such maximum to such minimum,each such variation lasting a length of time equivalent to the time forone bristle length of each filament to emerge from the bath wherebytapered sections of bristle length are formed, and without stopping themovement of the filaments bringing them to approximately constant anduniform speed of movement and hardening the coatings under a positivetension sufiicient to maintain the filaments taut while hardeningwhereby substantially straight filaments are produced, and subsequentlycutting the continuous filaments into bristle lengths.

2. A process as specified in claim 1 in which each of the filamentscomprise a plurality of strands and such strands are passed through asolution of plastic material sufficiently fiuid to impregnate thefilaments to bond the strands together and such plastic is permitted togel before the filaments are passed through the specified coating bath.

3. A process as specified in claim 1 in which the filaments afteremerging from the bath are straight and under tension until the coatingsgel, after which they are passed while still under tension to a heatingzone adapted to harden the coatings.

4. A process as specified in claim 1 in which the coating bath has aviscosity sufflcient to form prevented by maintaining over the surfaceof the bath a thin layer of controlled atmosphere adapted to reduce therate of evaporation from the surface of the bath below the normal ratewhich would take place if the surface were freely exposed to the air.

5. An apparatus for making tapered bristles to be used in conjunctionwith a coating bath of plastic material adapted to cling to thefilaments 12 plastic materials adapted to cling to the filaments toform'coatings of substantial thickness comprising a source of aplurality of core filaments, a container to hold such a coating bath,means for drawing the filaments simultaneously and substantiallyparallel into and out of the to form coatings of substantial thickness,compnsinga source of a plurality of core filaments, a container forholding such bath, means for passing such plurality of filamentsinto andout of such bath including means for intermittently varying the speed ofwithdrawal of the filaments from the bath and including means wherebythe speed of movement of the filaments may be brought to anapproximately constant and uniform speed without stopping the movementof the filaments, an oven in which the filament coatings can behardened, and means for moving the filaments through such oven at suchconstant rate of speed under a tension sufiicient to maintain thefilaments substantially straight while hardening.

6. An apparatus for making bristles for paint brushes and the likecomprising a, source from which a plurality of filaments can bewithdrawn under tension, a container for holding a coating bath and apreliminary drying oven associated therewith, a set 01' driven rollsadapted to draw the filaments through the bath and through such oven,means associated with such rolls whereby the speed of withdrawal of thefilament may be intermittently varied, a second oven in which the coatedfilaments can be hardened, a second set of driven rolls for drawing thefilaments through such second oven, and means for maintaining thefilaments under substantially greater tension in said second ovenbetween said two sets of driven rolls than that maintained on thefilaments while they are passing through the coating bath.

'7. An apparatus as specified in claim 6 which further includesmechanism associated with said first set of driven rolls whereby thespeed of movement of the filaments through the coating bath is varied insubstantially uniform cycles, while the filaments pass through thesecond oven at substantially uniform speeds.

8. An apparatus for making tapered bristles to be used in conjunctionwith a coating bath of coating bath, means for varying the average speedof the filaments simultaneously and means whereby the speed of thefilaments can be caused intermittently to vary back-and forth between aminimum and a maximum relative to such average speed.

9. The combination with an apparatus for producing artificial bristlescomprising a source of core filaments, a container for a coating bath, adrying oven, a baking oven and means for drawing the filaments fromtheir source and through the coating bath and baking oven, the filamentsbeing drawn out of the baking oven at approximately uniform speed, ofmeans whereby the speed with which the core filaments are withdrawn fromthe coating is alternately accelerated v and slowed down while the corefilaments are maintained substantially under tension from the coatingbath until they emerge from the baking oven, such speed-varying meanscomprising a roller over which the coated core filaments pass whichreciprocates back and forth in the approximate path from which thecoated core filaments are moving while remaining an approximatelyconstant distance from an adjacent roll towards which the coated corefilaments are moving.

HARVEY A. NEVILLE. THOMAS G. HARRIS. REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,077,492 Ritzert Apr. 20, 19371,697,236 Gingras Jan. 1, 1929 2,207,158 Neville July 9, 1940 1,234,704Subers July 24, 1917 2,267,597 Neville et a1. Dec. 23, 1941 2,274,542Griffiths Feb. 24, 1942 2,341,823 Smith Feb. 15, 1944 1,257,665 ArnoldFeb. 26, 1918 602,797 Annison Apr. 19, 1898 1,662,816 Bigelow Mar. 20,1928 2,220,958 Jennings Nov. 12, 1940

